For hundreds or even thousands of years, when an animal such as a horse, cow, sheep, dog, camel, etc. was to be sold, the purchaser had to rely, to a large extent, on the honesty of the seller to communicate accurately the health, age, abilities and pedigree of the animal.
Additionally, the purchaser could rely on his own experience and those physical traits that could be easily observed. For instance, age can be estimated by an inspection of the teeth by an experienced veterinarian, prior to the purchase of a horse. In addition, hooves and joint condition can be checked visually, the coat can be checked for overall condition and any parasites, and other traits can be evaluated physically, visually and behaviorally.
As technology and veterinary science has advanced, clinical laboratory testing can be used to help determine the parentage, health and any pertinent ongoing infections in the animal. Just as in humans, blood work can be done to assess the health of the animal such as measuring blood sugar levels, blood urea nitrogen, amylase, total calcium, and many other clinical lab values. Equipment manufacturers have also developed new equipment which can be configured to allow X-rays, CAT scans, PET scans and most other advanced imaging techniques with horses and other large animals. Various veterinary schools have advanced the understanding of clinical medicine pertaining to animals. For example, Auburn University College of Veterinary Medicine has instituted the Equine Health Research Program to improve equine health through high quality research.
However, these techniques are based on morphological characteristics that can be evaluated by observing and measuring existing structures of various tissues in the body as they currently appear. Based upon these observations and measurements, an evaluation of the physical condition and age of an animal can be made. However, these measurements don't provide any indication of the potential physical skills of the animals nor of the predisposition to future good health or demise. Furthermore, future health and physical problems can only be anticipated based upon existing clinical indicators and not predispositions to disease be they mental or physical.